[PATCH v2 2/2] Enable arch-specific CFI directives and DWARF instructions only when required by the target (part 1)

[Matthieu Longo]

On 2025-04-25 14:10, Jan Beulich wrote:
> On 25.04.2025 13:04, Matthieu Longo wrote:
>> --- a/gas/dw2gencfi.c
>> +++ b/gas/dw2gencfi.c
>> @@ -720,9 +720,16 @@ const pseudo_typeS cfi_pseudo_table[] =
>>       { "cfi_same_value", dot_cfi, DW_CFA_same_value },
>>       { "cfi_remember_state", dot_cfi, DW_CFA_remember_state },
>>       { "cfi_restore_state", dot_cfi, DW_CFA_restore_state },
>> -    { "cfi_window_save", dot_cfi, DW_CFA_GNU_window_save },
>> +#if TC_AARCH64
>> +    /* cfi_window_save is an alias of cfi_negate_ra_state which is kept for
>> +       backward-compatibility concerns.  */
>> +    { "cfi_window_save", dot_cfi, DW_CFA_AARCH64_negate_ra_state },
> 
> Why's this of concern only for Arm64?
> 

I am not sure that I understand what your question is here.
cfi_window_save is only used by AArch64 and Sparc.

>> --- a/gas/gen-sframe.c
>> +++ b/gas/gen-sframe.c
>> @@ -1257,6 +1257,8 @@ sframe_xlate_do_restore (struct sframe_xlate_ctx *xlate_ctx,
>>     return SFRAME_XLATE_OK;
>>   }
>>   
>> +#if TC_AARCH64
>> +
>>   /* Translate DW_CFA_AARCH64_negate_ra_state into SFrame context.
>>      Return SFRAME_XLATE_OK if success.  */
>>   
>> @@ -1287,30 +1289,7 @@ sframe_xlate_do_aarch64_negate_ra_state_with_pc (struct sframe_xlate_ctx *xlate_
>>     return SFRAME_XLATE_ERR_NOTREPRESENTED;  /* Not represented.  */
>>   }
>>   
>> -/* Translate DW_CFA_GNU_window_save into SFrame context.
>> -   DW_CFA_GNU_window_save is a DWARF Sparc extension, but is multiplexed with a
>> -   directive of DWARF AArch64 extension: DW_CFA_AARCH64_negate_ra_state.
>> -   The AArch64 backend of GCC 14 and older versions was emitting mistakenly the
>> -   Sparc CFI directive (.cfi_window_save).  From GCC 15, the AArch64 backend
>> -   only emits .cfi_negate_ra_state.  For backward compatibility, the handler for
>> -   .cfi_window_save needs to check whether the directive was used in a AArch64
>> -   ABI context or not.
>> -   Return SFRAME_XLATE_OK if success.  */
>> -
>> -static int
>> -sframe_xlate_do_gnu_window_save (struct sframe_xlate_ctx *xlate_ctx,
>> -				 struct cfi_insn_data *cfi_insn)
>> -{
>> -  unsigned char abi_arch = sframe_get_abi_arch ();
>> -
>> -  /* Translate DW_CFA_AARCH64_negate_ra_state into SFrame context.  */
>> -  if (abi_arch == SFRAME_ABI_AARCH64_ENDIAN_BIG
>> -      || abi_arch == SFRAME_ABI_AARCH64_ENDIAN_LITTLE)
>> -    return sframe_xlate_do_aarch64_negate_ra_state (xlate_ctx, cfi_insn);
>> -
>> -  as_warn (_("skipping SFrame FDE; .cfi_window_save"));
>> -  return SFRAME_XLATE_ERR_NOTREPRESENTED;  /* Not represented.  */
>> -}
>> +#endif /* TC_AARCH64 */
>>   
>>   /* Handle DW_CFA_expression in .cfi_escape.
>>   
>> @@ -1622,14 +1601,14 @@ sframe_do_cfi_insn (struct sframe_xlate_ctx *xlate_ctx,
>>       case DW_CFA_restore:
>>         err = sframe_xlate_do_restore (xlate_ctx, cfi_insn);
>>         break;
>> -    /* DW_CFA_AARCH64_negate_ra_state is multiplexed with
>> -       DW_CFA_GNU_window_save.  */
>> -    case DW_CFA_GNU_window_save:
>> -      err = sframe_xlate_do_gnu_window_save (xlate_ctx, cfi_insn);
>> +#if TC_AARCH64
>> +    case DW_CFA_AARCH64_negate_ra_state:
>> +      err = sframe_xlate_do_aarch64_negate_ra_state (xlate_ctx, cfi_insn);
>>         break;
>>       case DW_CFA_AARCH64_negate_ra_state_with_pc:
>>         err = sframe_xlate_do_aarch64_negate_ra_state_with_pc (xlate_ctx, cfi_insn);
>>         break;
>> +#endif /* TC_AARCH64 */
>>       case DW_CFA_register:
>>         err = sframe_xlate_do_register (xlate_ctx, cfi_insn);
>>         break;
> 
> This wants looking over by Indu (now Cc-ed).

FYI I removed DW_CFA_GNU_window_save following the suggestion of Jens Remus:
https://inbox.sourceware.org/binutils/08aa86e2-f1ba-49cf-a755-ecb7114308e5@linux.ibm.com/

> 
> Jan